Device and method for processing screw rotor, and cutting tool

ABSTRACT

A method for processing a screw rotor includes a step of rotating a blade holder  2  while shifting the blade holder  2  in X-axis, Y-axis, and Z-axis directions to form a groove on the outer surface of a rotating cylindrical workpiece  1  with a tool  3  using a processing apparatus having a bed  11 ; a C-axis shaft supporter  12  disposed on the bed  11 ; a C-axis shaft  14  held by the C-axis shaft supporter  12 , the C-axis shaft  14  for rotating the cylindrical object  1 ; a column  13  disposed on the bed  11 ; the blade holder  2  rotatably held by the column  13 ; and the tool  3  attached to the blade holder  2.

TECHNICAL FIELD

The present invention relates to an apparatus and a method forprocessing a screw rotor that is used in a refrigerant compressor or aircompressor, and to a cutting bit.

BACKGROUND ART

In known methods for processing screw rotors, a blank for screw cuttingis provided in a first shaft and tools are set in a second shaft whoserotational axis is orthogonal to that of the first shaft. These firstand second shafts are synchronously rotated by external means. At thebeginning of processing grooves, the entire tools are compressed in thesecond shaft. When the process proceeds, the tools are progressivelyexpanded out into a screw.

This is disclosed in PCT Japanese Translation Patent Publication No. Hei6-506640 (FIGS. 2, 3, 4, 5, 6, 7, 14 and the like), for example.

In the known processing methods, accuracy of finishing is compromiseddue to various factors such as groove size and installation position oftools, distance between the rotational axis of the first shaft and thatof the second shaft, or accuracy of the processing apparatus.Specifically, in a process using a forming tool, the cutting resistanceat the groove bottom is very large and thus micro-cutting, that is, 0.04mm in one cut at most is required. Furthermore, the entire cut lengthbecomes long, which exerts adverse effects on the improvement in theprocessing time and service life of the tool.

Furthermore, with the known methods for processing screw rotors, ifproduction of the particular processing apparatus intended forprocessing the screw rotor is discontinued, the screw rotor cannot bemanufactured.

Moreover, since grooves on the screw rotor have complex shapes, aspecial measuring device is necessary to measure the grooves. Therefore,in the known processing methods, a measuring step is provided as anadditional step. Accordingly, a workpiece is detached from theprocessing apparatus during the process and is measured to determinewhether the groove has predetermined dimensions. After the measurement,the workpiece is returned to the process.

To solve the above described problems, it is a first object of thepresent invention to provide a method and an apparatus for processing ascrew rotor in which a groove with a complex shape and the inner andouter surfaces of the screw rotor are efficiently processed with highaccuracy using a commercially-available five-axis NC machine tool and toprovide a cutting bit for use in the processing apparatus and method.

A second object of the present invention is to provide a method and anapparatus for processing a groove with a cutting depth that enables highprocessing efficiency, for the purpose of solving the problem of havinga small cutting amount in the process using the forming blade due tocutting resistance at the groove bottom.

A third object of the present invention is to provide a method and anapparatus for processing a screw rotor in which the accuracy of theshape of a groove, which is determined depending on the processingapparatus, arrangement, and tool in the known processing method andapparatus, can be readily modified.

A fourth object of the present invention is to provide a method and anapparatus for processing a screw rotor in which the accuracy of theshape of a groove processed by the apparatus can be measured andmodified, which is not possible with known processing apparatuses.

A fifth object of the present invention is to provide a method and anapparatus for processing a screw rotor in which both an inexpensivecommercially-available tool and an expensive special tool are used incombination to process the screw rotor so that the expensive specialtool can have a long service life and the overall expenses of the toolscan be reduced.

A sixth object of the present invention is to provide a method and anapparatus for processing a screw rotor in which the screw rotor isprocessed without a shaft, which is provided in the screw rotor in theknown methods, and thus costs of processing and facilities are reduced.

DISCLOSURE OF INVENTION

An apparatus for processing a screw rotor according to the presentinvention includes a bed; a C-axis shaft supporter disposed on the bed;a C-axis shaft held by the C-axis shaft supporter, for rotating acylindrical object; a column disposed on the bed; a rotatable bladeholder held by the column; and a tool attached to the blade holder,wherein the apparatus further includes a special shaft and aworkpiece-attaching member, the special shaft being connected to theC-axis shaft and rotating in synchronism with the C-axis shaft, theworkpiece-attaching member being connected to the special shaft androtating in synchronism with the special shaft.

A method for processing a screw rotor according to the present inventionincludes a step of rotating a blade holder while shifting the bladeholder in X-axis, Y-axis, and Z-axis directions to form a groove on theouter surface of a rotating workpiece using the aforementioned tool.This method includes a first step of roughly cutting the groove on theouter surface of the workpiece and a second step of shaving the sidesurfaces and the bottom surface of the groove.

According to the present invention, complex grooves are effectivelyprocessed with high accuracy under five-axis NC control. Furthermore,with the method according to the present invention, grooves areprocessed to have special shapes on their groove bottoms and variousspecial tooth shapes for a single screw can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the principal of a process formanufacturing a screw rotor.

FIG. 2 is a schematic view showing the principal of compression by ascrew compressor.

FIG. 3 is a partial cross-sectional view taken along line I-I′ in FIG.2.

FIG. 4 (A) is a structural front view of an apparatus for processing ascrew rotor and FIG. 4 (B) is a cross-sectional view of the apparatus.

FIG. 5 is a schematic view showing a state when a workpiece is attachedto an arbor.

FIG. 6 is a flowchart of steps for processing a screw rotor.

FIG. 7 is a conceptual view showing processing of the workpiece with anend mill.

FIG. 8 is a conceptual view showing processing of the workpiece with around-end mill.

FIG. 9 is a perspective view of a groove-side-shaving bit used in afirst embodiment.

FIG. 10 (A) is a front view of a blade of a bit and FIG. 10 (B) is anenlarged view of a blade edge.

FIG. 11 is a schematic view showing a relationship between a groove andthe groove-side-shaving bit.

FIG. 12 is a schematic view showing a relationship between the grooveand right and left cut angles.

FIG. 13 is a schematic view showing a relationship between the grooveand right and left cut angles.

FIG. 14 is a schematic view showing a clearance portion.

FIG. 15 shows profile lines of the side surfaces of a groove formed witha rotational circle.

FIG. 16 (A) is a schematic view of a known bit and FIG. 16 (B) is aschematic view of a groove-bottom-round-bit of the present invention.

FIG. 17 is a schematic view showing a relationship between the grooveand the bit.

FIG. 18 is a schematic view showing a relationship between the grooveand the bit.

FIG. 19 is a schematic view showing an automatic measurement of thewidth of a groove.

FIG. 20 is a schematic view of a groove-side-shaving bit used in asecond embodiment.

FIG. 21 shows a front view, a side view, and an enlarged view of theblade of the bit shown in FIG. 20.

FIG. 22 is a schematic view showing a relationship between the grooveand the groove-side-shaving bit according to the second embodiment.

FIG. 23 is a schematic view showing a relationship between the grooveand right and left cut angles according to the second embodiment.

FIG. 24 is a schematic view of a relationship between the groove andright and left cut angles according to the second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

The principle of a process for manufacturing a screw rotor according tothe present invention will now be described by referring to FIG. 1.

A workpiece 1 as a cylindrical blank for screw cutting rotates around anaxis (C-axis) that is a line connecting the center of the top surface(first flat surface) with the center of the bottom surface (second flatsurface). A blade holder 2 is disposed at the position orthogonal to theC-axis, namely, above the circumferential surface (outer surface) of theworkpiece 1. A tool 3 directing its blade towards the workpiece 1 isdisposed at the bottom of the blade holder 2. The blade holder 2 pivotsabout a B-axis and moves in a Z-axis direction parallel to the C-axis,in an X-axis direction that is a vertical direction, and in a Y-axisdirection that is orthogonal to both the Z-axis and the X-axis. Inaccordance with an NC program, the pivotal movement of the blade holder2 about the B-axis and the movement of the blade holder 2 along theX-axis and Z-axis are combined in association with a predeterminedrotation speed of the workpiece 1 around the C-axis. Accordingly, thetool 3 is rotationally moved about a reference point 4 to form a grooveon the outer surface of the workpiece 1. The ratio of the circularmovement of the tool 3 and the rotational movement of the workpiece 1about the C-axis is 6:11, and these movements are synchronized. The tool3 is protracted stepwise during the movement of the tool 3. Therefore, aradial length 26 of the tool 3 at the beginning of the process ischanged to a radial length 27 at the completion of the process.

The principal of general compression by a screw compressor will now bedescribed with reference to FIG. 2.

The screw compressor includes a screw rotor 1 with six grooves 9 andgate rotors 8 a and 8 b each having eleven teeth 10 to engage thegrooves 9. The gate rotors 8 a and 8 b are symmetrically provided on theright and left sides of the screw rotor 1 in the direction orthogonal tothe axis of the screw rotor 1. When the screw rotor 1 rotates, a grooveof the screw rotor 1 expands and a refrigerant gas is sucked into thegroove. When the screw rotor 1 keeps rotating to reach the maximumvolumes of the groove, the groove is trapped by the gate rotors 8 a and8 b. Thereafter, when rotational movement of the screw rotor 1 furtherproceeds, the volumes of the groove is reduced to compress therefrigerant gas.

FIG. 3 is a fragmentary cross-sectional view taken along line I-I′ inFIG. 2, showing a state when the gate rotor 8 a is engaged with thescrew rotor 1.

A processing apparatus to realize the above-described principal of theprocess will now be described by referring to a schematic view of thestructure of the apparatus in FIG. 4. FIG. 4 (a) is a front view of theprocessing apparatus, and FIG. 4 (b) is a longitudinal cross-sectionalview taken along line II-II′ in FIG. 4 (a).

Referring to FIG. 4, the processing apparatus includes a bed 11, aC-axis shaft supporter 12 disposed on the bed 11, a column 13, a C-axisshaft 14 rotatably supported by the C-axis shaft supporter 12, a bladeholder 2 pivotably disposed on the side face of the column 13 close tothe C-axis shaft supporter, and the tool 3 attached to the bottom of theblade holder 2. Regular five-axis NC machine tools also have theaforementioned structure.

In the processing apparatus, a special shaft 15 is provided at the endof the C-axis shaft 14 and thus the length of the shaft rotating aboutthe C-axis is increased. An arbor 16 is disposed at the end of thespecial shaft 15 and the workpiece 1 is attached to the arbor 16. Sincethe special shaft 15 protrudes long from the C-axis shaft supporter 12,the special shaft 15 cannot provide sufficient accuracy due to itssensitivity to vibration. Therefore, preferably, the special shaft 15 issupported by a shake stopper 17.

A movable tail stock 18 is provided on the bed 11 and can be movedlaterally. When the outer surface of the workpiece 1 is processed, themovable tail stock 18 supports the flat surface of the workpiece 1remote from the special shaft 15 and turns in association with themovement of the C-axis shaft 14. When the inner surface of the workpiece11 is processed, the column 13 is tilted to move the blade holder 2 to aposition 2′. In this case, the movable tail stock 18 is moved to the endof the bed 11 to avoid interference with the column 13.

FIG. 5 is a schematic view showing the state where the workpiece 1 isattached to the arbor 16. The arbor 16 is provided with a plurality ofbolts 19. By inserting these bolts 19 into the workpiece 1, theworkpiece 1 is fixed to the arbor 16. The side of the arbor 16 oppositefrom the side from which the bolts 19 protrude (the side close to thespecial shaft 15) is tapered. A pull stud bolt 20 disposed on thetapered end of the arbor 16 is inserted into a hole of the special shaft15 and is strongly pulled by a pulling device 21, whereby the arbor 16is securely fixed in the hole of the special shaft 15. At this time,centering is also performed.

Next, steps of processing a screw rotor using the aforementionedprocessing apparatus will be described by referring to the flowchartshown in FIG. 6. A series of steps is performed in accordance with theNC program previously input.

First of all, the inner surface of the workpiece 1 is processed (step1). Step is referred to as “S” hereinbelow. An inner-surface-processingbit is used to process the inner surface of the workpiece 1. In thisstep, the blade holder 2 is moved to the position 2′ in FIG. 4(a) andthus the movable tail stock 18 is disposed at the end of the bed 11.

When processing of the inner surface is completed, the movable tailstock 18 is moved along the bed 11 to support the workpiece 1 (S2).

Next, rough cutting of a groove is performed on the outer surface of theworkpiece 1 (S3). In this step, since a groove is processed on the bareouter surface with an end mill, an automatic tool changer replaces theinner-surface-processing bit used in S1 with the end mill. FIG. 7 is aconceptual illustration, showing a state where the end mill processesthe workpiece 1.

When a wide groove is processed or a groove needs to be processed withhigh precision, an end mill may be reciprocated at a small diameter.

Next, rough cutting is performed to form a round bottom of the roughgroove on the outer surface of the workpiece 1 (S4). In this step, theend mill used in S3 is automatically changed to a round-end mill (thetip of the end mill is rounded). FIG. 8 is a conceptual illustrationshowing a state where the workpiece 1 is processed by the round-endmill.

Next, finishing of the outer surface of the workpiece 1, that is,shaving on the bare areas of the column where no groove is provided isperformed (S5). In this step, the round-end mill used for S4 isautomatically switched to an outer-surface-processing bit.

Next, finishing of the left side of the groove (S6) and finishing of theright side of the groove (S7) are performed. In these steps, theouter-surface-processing bit used for S5 is automatically switched to agroove-side-shaving bit.

FIG. 9 is a perspective view of a groove-side-shaving bit 40. This toolis used for a shaving process performed at a cutting feed rate with theshaft fixed (irregularities on the surface are shaved off). Therefore,the groove-side-shaving bit 40 is placed by shifting the phase by 27°with respect to the orientation of the shaft and is attached to acommercially-available tool holder 41 for use. The groove-side-shavingbit 40 has a right blade 42 and a left blade 43. FIG. 10 shows theportion of the blade. Commercially-available throw-away chips are usedfor the blades. Since these blades each have a rake angle of 20° and a4-mm-long parallel blade 44, the cut angle and cut depth are improved.

FIG. 11 shows a relationship between the groove and the right blade 42and the left blade 43 in the groove-side-shaving bits 40, in a rightside finishing process and a left side finishing process.

In the processes, the blade edges have to recede by 1 mm from therotational axis of the workpiece. Therefore, the Y-axis and the Z-axisof the processing apparatus are aligned to Y1 and Z1 when processing theleft side and to Y2 and Z2 when processing the right side. Since theblades each have a structure shown in FIG. 10, left cut angles 45 a and45 b are in the range of 120° to 93°, whereas right cut angles 46 a and46 b are in the range of 93° to 120°, as shown in FIGS. 12 and 13. Inthis way, the right and left blades can be operated under the samecutting conditions.

FIG. 15 shows profile lines of the side surfaces of a groove formed witha given clearance circle. In FIG. 15, lines 100 a and 100 b aretheoretical lines calculated at a theoretical synchronous ratio, and thelines 101 a and 101 b are profile lines having errors processed by aknown method. The lines 101 a and 101 b cannot be processed with theknown method but can be processed with the aforementionedgroove-side-shaving bit for the right and left side surfaces.

Next, measurement of the groove width is performed (S8). The processingapparatus includes an automatic measuring system for arbitrarymeasurement of the object at the beginning of a process, or forperiodical measurement during the process. When the measurement of thegroove width is selected, the groove width is measured (S9). FIG. 19shows a state of measuring the groove width. The measurement isperformed by a contact-measuring device 55, which is typically used intool machines. The measuring device 55 is automatically attached to ashaft 2 a of the blade holder 2 pivotal about the B-axis. The measuringdevice 55 measures the groove width of the processed portion under thesame movement control as that of the processing principal (X-, Z-, B-,C-, B-axis movement control). The measurement is automatically performedby an automatic measuring program for the groove width. The measuringprogram instructs the measuring device 55 to measure the width, thedepth, and the index angle of the groove. By this instruction, a tipprobe 56 of the measurement device is inserted into the groove 9 to comeinto contact with the groove 9 in the workpiece 1, thereby obtainingpositional information. This positional information is then processed toobtain the measurement result. The accuracy of the process is evaluatedbased on the data of the groove width. When the evaluation exceeds thepredetermined range, the process returns to S6 as indicated by an arrow35 to input a corrected value, and then S6, S7, S8, and S9 are performedagain in this order. When the evaluation falls within the range, theprocess proceeds to S10. If the process is stable, S9 may be omitted(arrow 36).

Next, rounding finishing of the groove bottom is performed (S10). Inthis step, the touch-probe measuring device 55 used for S9 or thegroove-side-shaving bit 40 used for S7 is replaced by a groove-bottomround-bit 110. In this step, the groove bottom is rounded by shaving.

When the grooves of the screw rotor 1 shown in FIG. 3 are engaged withthe gate rotor 8 a, thermal deformation occurs due to the difference intemperature between the entrance and exit of the refrigerant gas. Sincethe gate rotor 8 a is made of plastic, the outer surface of the screwrotor 1 comes into contact with the gate rotor due to the thermalexpansion and is shaved off, and thus the gap between the outer surfaceof the screw rotor 1 and the gate rotor is increased. This is one factorfor degraded performance.

In this process, preferably a clearance portion is formed in a grooveedge 50 shown in FIG. 3. As shown in FIG. 14, provision of a clearanceportion 51 makes the gate rotor 8 a capable of being shifted optionallyby a distance 52 in the direction indicated by the arrows. In this way,the outer surface of the screw rotor 1 is not shaved, thereby realizingalmost ideal engagement of the outer surface of the screw rotor 1 andthe gate rotor. This process can be sequentially performed by inputtingthe radius and the coordinates of the rotational axis in the NC program.

Even though the bit 110 of a known type shown in FIG. 16 is used in S6and S7, the amount of cut can dramatically be increased from 0.04 mm to0.5-2 mm. However, due to the change in contact angle inherent in asingle screw rotor (45° to 72°) and the difference in cut angle betweenthe right and left blades, desired surface roughness cannot beaccomplished by the known bit. More specifically, as shown in FIGS. 17and 18, left cut angles 120 a and 120 b are in the range of 135° to108°, whereas the right cut angles 121 a and 121 b are in the range of43.5° to 72°. Accordingly, the right blade may chafe the outer surfaceduring the cutting process. Furthermore, since the clearance angle ofthe left blade is made large so as to prevent the left blade fromcontacting with the workpiece, the angle of the left blade edge is 43°at most, resulting in decreased strength. Therefore, the left blade hasa disadvantage in that it cannot tolerate a high feed rate. By contrast,according to the present embodiment, the above-described disadvantagesare overcome by the use of the tool shown in FIG. 9 in S6 and S7.Furthermore, in S6 and S7, since a tool used for the narrow groove widthcan also process a wide groove, only a single tool is necessary,resulting in reduced costs as compared to using an expensive formingtool bit.

When the groove width is modified with a known special-purposeprocessing apparatus, the width of the forming tool bit needs to becontrolled. Further, the dimensional accuracy of the groove varies dueto the accuracy of the processing apparatus and deterioration inaccuracy of the processing apparatus over time, whereby it is difficultto control the dimensional accuracy of the groove. Furthermore, backlashof the processing apparatus in accordance with the processing principlecauses the blade to slip and thus the desired shape cannot be formed. Bycontrast, according to the present invention, the rough processing isperformed at first and then the side surfaces of the grooves arefinished with the blades having different angles, whereby slipping ofthe blades hardly ever occurs. Furthermore, the groove width can bemodified by the use of the NC processing program.

Furthermore, the groove bottom is roughly processed with a groove-bottomround-end mill shown in FIG. 8 and is then finished with thegroove-bottom round-bit of a known type shown in FIG. 16 (A), wherebythe amount of the groove-bottom shaved in finishing is 0.2 mm or less.Accordingly, the process is performed with the minimum number of cuttingsteps, thereby contributing to decreased processing time.

Since a process of rounding the groove bottom has large cuttingresistance, the tool has to have high strength. A blade edge 111 of thebit shown in FIG. 16(A) is brazed and thus has a decreased strength dueto the influence of heat. By contrast, when a throw-away-chip-type bladeedge 113 that can be clamped with a bolt 112, as shown in FIG. 16(B), isemployed, the bit has increased strength, thereby improving the cuttingefficiency. In this case, the chip is positioned by a slit 114.

A single groove is formed in a series of processes from S1 to S10 andalso the other grooves are sequentially processed using the toolsdescribed above. If a series of steps shown in FIG. 6 is programmed as areference processing program and required processes and tools are calledup optionally to process the other five grooves, the program can beshortened.

The standard process of a screw rotor has a design of 6 parallel groovesof the screw for 11 teeth of the gate rotor and this design is fixed ina known special-purpose apparatus. However, according to theabove-described processing apparatus and process, a specific groove andtooth arrangement, such as 5 grooves of the screw for 7 teeth of thegate rotor can be realized. The processing apparatus of a known type isspecially built for a particular process and thus is only used for onetype of tooth shape. On the other hand, the process of the presentinvention can deal with various types of tooth shape and thus there ispossibility of new tooth designs.

Second Embodiment

In the first embodiment, priorities are given to the accuracy of theprocessing apparatus and processing, and thus the process in a singledirection with the groove-side-shaving bit shown in FIG. 9 is described.If a processing apparatus can exhibit the same accuracy in areciprocating process as that in the single-direction process, thereciprocating process can utilize the time for the tool to return,thereby further reducing the processing time. FIG. 20 shows agroove-side-shaving bit that realizes this reciprocating process.

FIG. 20 is a perspective view of areciprocation-type-groove-side-shaving bit 60 inserted into a shaft 25of the B-axis blade holder. This tool is used for shaving at a cuttingfeed rate with the shaft 25 fixed. Therefore, astandard-for-oblique-view 61 is provided in order to shift the phase ofthe tool by 27° with respect to the orientation of the shaft. This toolcan be attached to a commercially available tool holder 41 for use.

The reciprocation-type-groove-side-shaving bit 60 is provided withsymmetrical throw-away-chips 62 and 63 shown in FIG. 21. Each of thechips 62 and 63 is composed of a commercially-available throw-away-chip,and a flank 64 has a rake angle of 20°, which is the most distinctivefeature of this embodiment. A parallel blade 65 measures 4 mm in length.The rake angle is provided at the rake surface 66 in the firstembodiment but is provided on the flank 64 according to the presentinvention and thus the chip is symmetrical. Therefore, the tool haslarge thicknesses 67 and 68, thereby increasing the strength of thetool. Furthermore, with this structure, deformation in the tool iseliminated and thus increased cut-depth and a high-speed cutting feedrate are accomplished.

FIG. 22 shows a relationship between the groove and a right blade 62 anda left blade 63 in the reciprocation-type-groove-side-shaving bit 60 inthe finishing process of the right and left side surfaces.

In this process, the blade edges need to be recessed by 1 mm from therotational axis of the work. This is accomplished by aligning the Y-axisand the Z-axis of the processing apparatus to Y1 and Z1 in processingthe left side and to Y2 and Z2 in processing the right side. Since theblades have the structures shown in FIGS. 23 and 24, left cutting angles45 a and 45 b are in the range of 1200 to 93°, whereas right cuttingangles 46 a and 46 b are in the range of 930 to 120°. Therefore, theright and left blades of the present embodiment can performreciprocating cutting under the same blade edge conditions, similar tothe first embodiment.

To confirm the effects of the process with thereciprocating-groove-side-shaving bit, experimental processes accordingto a known method and the first and second embodiments are performed. Inthese experiments, only the time for processing the side surfaces of thegrooves is compared, not the entire processing time.

(Evaluation of a Process for Forming 6 Grooves Each Having a Length of215 mm and a Depth of 40 mm, for Example)

-   Known method: cut depth, 0.04 mm; feed rate, 9000 mm; return rate,    9000 mm/min; the number of cuts, forward movement, 40/0.04=1000,    backward movement 40/0.04=1000, total of 6-grooves, 12000;-   reciprocating processing time, 215*2/9000*1000=47.7 min; total    processing time for 6 grooves, 47.7 min*6-grooves=286 min-   First embodiment: cut depth, 2 mm; feed rate, 3000 mm/min; return    rate, 9000 mm/min; the number of cuts, forward movement, 40/2=20,    backward movement 40/2=20, total of 6-grooves, 240; one-way    processing time for right and left sides, 215/3000*20*2=2.86 min;    returning time, 215/9000*20*2=0.95 min; total processing time,    2.86+0.95=3.81 min;-   total processing time for 6 grooves, 22.9 min-   Second embodiment: cut depth, 3.5 mm; feed rate, 9000 mm/min; return    rate, 9000 mm/min; the number of cuts, forward movement, 40/3.5=12,    backward movement, 40/3.5=12, total of 6 grooves, 144; reciprocating    processing time for right and left sides, 215*2/9000*12*2=1.14;    total processing time for 6-grooves, 6.9 min

These results confirm that the number of positioning and the loss timeare improved drastically, thereby improving the processing efficiency inthe second embodiment. The number of the reciprocating movements at ahigh moving rate is halved, resulting in long service life of thesliding surface.

REFERENCE NUMERALS

-   -   1 workpiece (screw rotor), 2 blade holder, 3 tool, 8 gate rotor,        9 grooves, 10 teeth, 11 bed, 12 C-axis shaft supporter, 13        column, 14 C-axis shaft, 15 special shaft, 16 arbor, 17 shake        stopper, 18 movable tail stock, 19 bolts, 20 pull stud bolt, 21        pulling device, 40 groove-side-shaving bit, 41 commercially        available tool holder, 42 right blade, 43 left blade, 44        parallel blade, 45 cut angle, 51 clearance portion, 55 contact        measuring device, 60 reciprocation-type-groove-side-shaving bit,        61 standard-for-oblique-view, 62 right blade, 63 left blade, 100        theoretical line, 101 line processed by a known method, 120 left        cut angle, 121 right cut angle

1. An apparatus for processing a screw rotor, comprising a bed; a C-axisshaft supporter disposed on the bed; a C-axis shaft held by the C-axisshaft supporter, for rotating a cylindrical workpiece; a column disposedon the bed; a blade holder rotatably held by the column; and a toolattached to the blade holder, wherein the apparatus further comprises aspecial shaft and an workpiece-attaching member, the special shaft beingconnected to the C-axis shaft and rotating in synchronism with theC-axis shaft, the workpiece-attaching member being connected to thespecial shaft and rotating in synchronism with the special shaft.
 2. Theapparatus according to claim 1, further comprising a shake stopperdisposed on the bed, the shake stopper supporting the special shaft. 3.The apparatus according to claim 1, further comprising an automaticmeasuring system for measuring the width of a processed screw groove. 4.A method for processing a screw rotor comprising a step of rotating ablade holder while shifting the blade holder in X-axis, Y-axis, andZ-axis directions to form a screw groove on the outer surface of arotating cylindrical workpiece with a tool, using a processing apparatuscomprising a bed; a C-axis shaft supporter disposed on the bed; a C-axisshaft held by the C-axis shaft supporter, for rotating the cylindricalworkpiece; a column disposed on the bed; the blade holder rotatably heldby the column; and the tool attached to the blade holder.
 5. The methodaccording to claim 4, wherein said step to form a screw groove includesa first step of roughly cutting the groove on the outer surface of theworkpiece and a second step of shaving the side surfaces and the bottomsurface of the groove.
 6. The method according to claim 5, wherein thefirst step comprises a sub-step of cutting the groove using an end milland a sub-step of rounding the bottom of the groove using a round-endmill.
 7. The method according to claim 5, wherein the second stepcomprises a sub-step of shaving the side surfaces of the groove using ashaving bit for the side surface of the groove and a sub-step of shavingthe bottom surface of the groove using a round bit for the bottom of thegroove.
 8. The method according to claim 5, wherein shaving is performedin one direction in the second step.
 9. The method according to claim 5,wherein shaving is performed in a reciprocating manner in the secondstep.
 10. The method according to claim 4, wherein the method includes ameasuring process to automatically measure the width of the processedgroove during or at the completion of the process.
 11. A shaving bit forthe side surface of a groove, wherein replaceable blades are disposed atright and left edges of the shaving bit, wherein the blades each have arake angle of about 20° with respect to a surface adjacent to a flank.12. A shaving bit for the side surface of a groove, wherein replaceableblades are symmetrically disposed at right and left edges of the shavingbit, wherein the blades each have a rake angle of about 20° at a flank.13. A round bit for the bottom of a groove wherein a replaceablethrow-away-chip blade is fixed with a clamping bolt.